More and more these days, Solar Panels or other renewable energies such as Heat Pumps are being combined with solid-fuel and back-boiler systems. Either as a new build, or as part of a retrofit. It wouldn’t be unusual to have a system combining solar, an oil boiler and a solid fuel stove into the one tank – one like in the diagram below:

Both the solar and the boiler circuit are pumped circuits – water is pushed around them by a circulating pump. The stove circuit is different; there’s no pump. For safety reasons it uses a gravity flow to heat the tank. The temperature difference between a hot stove and a cooler tank creates a natural circulation of water between the two. This is sometimes called a Thermosiphon.

This, however, can cause some unusual problems.

The Cold Stove Problem.

On good days the solar panels will heat the bottom of the tank, warming the water inside. On other occasions, this water may be heated by the boiler. Especially if it is warm out, the stove will likely not be lit – so will stay cold. In the diagram above, its outlet temperature is a cold 20°C.

The temperature difference between the heated water in the tank and the unlit and still cold stove will be high enough that circulation between the two begins. This is the same Thermosiphon effect, but operating in the reverse direction. The cold stove will begin to leach heat out of the tank, cooling it down. This heat is lost either up the flue, or into the air in the room where the stove is located

If this heat came from your solar panels, then you will have to make up for the loss with an immersion heater or by calling in the oil boiler. If it came from your boiler alone, then you will have to run your boiler for longer.

Either way this is costing you money. And nobody likes the surprise that comes from turning on what was expected to be a nice-hot shower, only to be met by a rush of lukewarm at-best water.

A Solution?

It seems like the quick and easy solution is to simply swap the solar and stove heating connections at the tank. This will mean that the stove is now heating the entire tank from the bottom. The solar will now only heat the top half of the tank. The modification would look like this:

The bottom of the tank will remain cool unless the stove is lit, meaning there will be no temperature difference to start the Thermosiphon. This solves the Thermosiphon problem, but introduced a new one.

This approach effectively halves the amount of hot water available from the solar panels. Whatever would’ve been lost to the Thermosiphon, is never received in the first place. Instead of losing hot water, now you never have it. Also, if this is a modification to an existing system, you would have to factor in the cost of hiring a plumber to do the work, or the time to do it yourself. Three to Five hours would be a good minimum for a skilled plumber.

Clearly, not an ideal solution. It solved one problem, but in a way creates another one in the process.

The Greentherm Way.

At Greentherm, we’re an engineering company first and foremost. We’re all engineers here. What this means is, we’re always looking for the best solution to a problem. Both in terms of cost-effectiveness, and long-term efficiency.

A customer came to us with a Thermosiphon problem on their system. This was the solution we offered:

A Solid Fuel Loading Valve

A Solid Fuel Loading Valve is a device which is designed to automatically regulate the flow of water coming out of a solid-fuel boiler or stove. The purpose of the loading valve is to allow the stove to heat up quicker and burn hotter, reducing coking of the flue and minimising internal corrosion. It does this by diverting the flow of water coming from the stove back towards the stove in a short loop, bypassing the rest of the heating system.

This diagram shows how the valve operates. When cold, the valve switches to divert, recirculating water back to the stove rather than through the tank:

When it warms up, the valve switches open, allowing water to flow to the tank, as seen below.

But what relevance is this to our Thermosiphon problem?

When the solid fuel stove in the above system is cold, the Loading Valve will be closed. It will effectively isolate the stove in its own short loop until the stove heats up. This means that cold water in the stove cannot flow towards the tank. This also means that warm water from the tank cannot flow back to a cold stove.

Therefore, the modification we ultimately made to the original system above, looked like the following:

If the stove is cold, the valve is switched to divert. When the stove is lit the valve will open once the water has reached a high enough temperature, allowing heat to move up from the stove to the tank. If the stove cools down, the valve closes, preventing circulation through the tank.

It’s that simple.

In a nutshell

Fitting a solid fuel loading valve to the system eliminated heat losses from a Thermosiphon. The efficiency of the system was improved. The Loading Valve also improved the combustion efficiency and lifespan of the stove by fulfilling its original function.

Physically adding the valve and divert loop took a competent plumber two hours. Including the cost of materials, this solution not only worked out cheaper for the customer to implement, but left her with a much more efficient system to boot.

Most importantly, this solution is safe*. The Solid Fuel Loading Valve is fully automatic. It isn’t reliant on electrical power or any external control unit- it’s operated solely by the heat in the water. This valve won’t be left stuck in position by a power failure, or quietly forgotten when the homeowner goes to sleep.

Problem?

Contact Us now to see how we can provide similar solutions to your heating and renewable energy problems.

If you have the same problem with a system loosing heat through a cold gravity circuit purchase Solid Fuel Loading Valves from us here, and implement the above solution yourself.

*Provided the System has been installed in accordance with regulations and industry best-practices.

Multi-Energy Jaspi 500L Thermal Store.

Only €1175!^*

Tanks, built like a Tank.

• Heavy Duty Construction

Jaspi Thermdal Stores are manufactured from thick sheets of high-quality steel, guaranteeing a long, leak-free service life under demanding conditions.

• Suitable for Heat Pump, Solid Fuel and Solar

Flexible tappings allow for the combination of any domestic heat sources for maximum efficiency and reliability. An internal baffle ensures that low temperature heat sources in the tank bottom will always have work to do.

• Domestic Hot water and Central Heating storage in one tank

A pair of indirect domestic hot water coils instantaneously create hot water only as it is needed, for maximum system efficiency.

• Leak Detecting Tappings

All tappings complete with Leak-Detect couplings, making any problem with sealing on installation clearly visible, verifying the integrity of the installation.

• Space Efficient Design

Designed specifically to fit through the average household door and maximise storage volume using the minimum amount of space.

• Insulation Ensures Efficiency

Designed with frigid Finland winters in mind. Each Store comes with high-density Polyurethane foam insulation, baked on for outstanding efficiency and thermal performance.

• Experienced engineering support.

We know our products and understand the customer’s needs. We have the in-house know-how to do what it takes to ensure your specifications are met.

• Special Introductory Pricing available Until December 31^st

Click Here to visit our online store and order.

Peace of Mind is Priceless.

There is nothing more expensive than a cheap thermal store. What’s saved in the purchase price is quickly lost to recalls, repairs and replacements. No matter your application, your Jaspi Hybrid thermal store can be trusted to give decades of hassle-free service.

Call us now, at 01 5314781 for no-obligation sales and technical inquiries. For more detailed information on the Jaspi range, send a message to info@greentherm.ie.  Visit our website at www.greentherm.ie for more information on other products we offer.

-The Greentherm Team

*Until June 30th 2017. Terms and conditions apply

Will it Fit? Cylinder Sizing and You

In our first post, we compared two different heat-sources, a heat-pump, and a condensing boiler. We took a look at the different performance characteristics, capabilities and expected running costs of each

In our second, we saw how the choice of heat-source could affect the temperatures we store water at, and what affect changing the storage temperature had on the amount of water we needed to store to get the same performance from the system.

Here in our final post, we will have a look at one of the most important components in a Greentherm central heating system; the buffer tank, Thermal Store or Combi-Cylinder.

We’ve already seen that to efficiently meet the hot water demands of a  modern home, the cylinder has to be far larger than the traditional copper tank tucked away in the hot-press.

The actual amount of storage required is calculated by us here at Greentherm as part of our design process. Based on the plans supplied to us by your architect, we calculate the heat load and hot water demands for your home and match them with a heat source capable of delivering the required performance. We then size the buffer tank based on the most efficient operating point of this source and the demands we have calculated.

This is a fairly involved process the details of which go far beyond this post, especially when modern regulations such as Energy Performance and Carbon Performance have to be accounted for.

For argument’s sake let’s assume that, based upon the plans and specifications we’ve received from your architect, we’ve calculated you need a 1000 Litre Thermal Storage tank to meet your new home’s hot-water and heating requirements.  How much space would that take up?

It certainly won’t fit in with the towels, so somewhere else must be found.

We recommend that a dedicated plant-room be set aside for your hot water storage and heating systems, both for ease of maintenance, ease of access and for your convenience.

This dedicated plant room will have to be large enough to accommodate the Thermal Store and its plumbing. So, how large will it have to be to fit our specified Store inside?

A simple way to estimate your cylinder dimensions

The Volume we require to store 1000 Litres of water is, conveniently, 1m³. A cube-shaped tank, 1 Metre by 1 Metre by 1 Metre will be large enough to hold 1000 Litres of water. Unfortunately for us it’s not that simple; the majority of Thermal Stores are cylindrical.

The basic geometrical formula for the volume of a cylinder is πR²H.

π is a constant that relates the circumference of a circle to its radius length. It can be taken for our purposes as having a value of 3.14

H, or the Height of the cylinder will generally be limited to the ceiling height of your home, less approximately 200mm for headspace to simplify installation.

R, is the radius of the cylinder – or the distance from the centre of the cylinder to its outer wall. It is important that the depth of insulation not be included in this.

To know the space required for the cylinder in the room, we re-arrange the above formula to give:

R = √(V/πH)

Assuming we have enough room to fit a 1.8 metre tall cylinder in the room

For a 1000L tank, R = √(1/3.14×1.8),

This calculates out to a cylinder radius of approximately 43cm.

This gives a total vessel diameter of nearly 90cm. On top of this, most cylinders will have an insulation blanket that also needs to be accounted for. An extra 5cm on each side of the cylinder for insulation means a 1000 Litre cylinder will be at least a metre wide when finished.

This is too wide to fit through most doors unless you opt for a tank such as the Jaspi Oval tank which has been specifically designed to fit through a standard doorway.

It will be necessary to allow for sufficient clearance around the sides of the cylinder for proper plumbing access. Depending on the works required, at minimum this could be another 30-50cm, meaning a 1000 Litre cylinder could require up to 1.3M of space in a room to comfortably install and plumb.

This will, of course, require some special arrangements to install, to ensure the cylinder will fit.

These special arrangements will need to be discussed with your architect in the design and specification phase.

The normal capacity we would usually install would be normally be in the range of 500 to 800 for a buffer tank, and typically up to 900 L for a combi-cylinder – so 1000 Litres is a little on the large side, but still within the realms of possibility.

That brings us to the end of this short series of postings, we hope you’ve found them informative. Contact us if you have any queries or questions on what we’ve gone through in this series, we’ll be more than happy to answer them.

In our previous post, we looked at a quick comparison between a Heat Pump, and a Boiler. We saw that a boiler was capable of providing heat very quickly, heating a cylinder up to temperature faster than a heat pump. At the same time we saw that using the Boiler to heat water was more expensive than using a Heat Pump, nearly three times the cost if Night-Rate electricity is  used.

The point was also made that a heat pump would be more efficient operating at 35°C, rather than 55°C. So why not store water at 35°C, rather than 50 or 60°C?

The Advantage of lower storage temperatures:

Storing water at lower temperatures brings a number of efficiency benefits. This is especially important with a heat pump because heat-pumps get less efficient, the higher the required water temperature gets

A hidden advantage comes in the form of heat loss. A fundamental principal of physics is that energy will always try to move from the hottest point in a system to coldest, and that the rate of heat loss will be proportional to the temperature difference between the two. What this means is that, the hotter your water storage cylinder, the more heat energy will be lost from it.

In older homes, the reason the Hot Press was Hot was poorly lagged hot water cylinders acting as heaters. In newer homes with insulated cylinders, heat loss from standing water will make a significant impact, especially if hot water is left standing for long periods of time.

Losses within distribution pipework are also reduced by operating at 35°.

What can low temperature water actually do?

Greentherm Underfloor Heating systems are specifically designed to operate efficiently at temperatures of 35°C.

The heat output of a system is also directly proportional to the surface area of the heat emitter and its temperature. The larger the area and the hotter it is, the more heat energy it will transfer.

To heat a room a certain amount of heat is required to maintain a comfortable temperature. The amount required depends on the set temperature of the room, the quality of the room’s insulation, the external temperature and how well ventilated the room is. The resulting heat input called the Heat Load, and performing a calculation of the expected heat load on a room is part of the process we go through at Greentherm when specifying a heating system for your home.

35°C would be too low a temperature for a conventional radiator system to meet the required Heat Load of most rooms. There would not be a large enough surface area to transfer energy fast enough.

A low temperature over a large floor area is more than capable of quickly and efficiently heating a room up to temperature. Other technologies, such as low-temperature radiators, or fan-coil radiators enable the use of low-temperature heating system water. However, the use of each of these creates new specific design considerations.

So, how much water do I need to store?

With high-temperature water, you will generally need a smaller hot water storage cylinder than with low temperature water. The usual strategy is to blend in an amount of cold water to reduce high-temperature water to a comfortable and safe temperature. This can be achieved through the use of a thermostatic mixing valve. The most common example of this would be a shower.

Showers will generally use upwards of 10 litres of water every minute. Some rain-head showers have consumptions that exceed 18 Litres per minute. In the table below is a quick comparison of the hot water requirements for a 10 minute shower, supplying 18 Litres per minute of water at a comfortable set temperature of 38°C. Two different supply temperatures are shown; for a heat-pump and for a boiler, using the maximum storage temperatures from our previous post. For the boiler, that will be 60°C. For the Heat Pump, 50°C without using the immersion heater.

From here on it should be clear that to work out the required water consumption, you should multiply the required hot water per shower, by the amount of showers to be taken. The addition of teenagers to the household could more than double the required amount per-shower. The addition of Zypho waste-water heat recovery units can reduce hot water requirements by up to a third, as detailed in a previous post.

For a four-person household with a boiler system we would need a minimum of 400 Litres of hot water storage to keep from running out of hot water. With a heat pump system, we would need at least 500 Litres. The addition of a solar coil to a storage tank can take up an additional 100 Litres of capacity that is not accessible to either boiler or heat-pump – in which case this capacity will have to be added to the figures above.

We can therefore see that a 4-person household fitted with rainhead showers, a storage tank capacity of up to 600 Litres could easily be required when a heat pump is fitted, and when it is operating at 50°C.

Once this water has gone, you’re relying on the ability of your heating system to recover the temperature of your domestic hot water. As we’ve seen previously, this can take some time.

And what about my heating system?

The design of your heating system can also affect the amount of water you need to store.  For modern designs of heating system your hot water cylinder acts as a thermal store of heat energy, similar to how a battery stores electricity. It will be providing both your hot water and the heat for your central heating system. How much water you will need to store depends not only on your domestic hot water requirements, but also the heat load on your central heating system, whether you have underfloor heating, radiators or some combination of bother, and what sources of heat you have installed.

This is a calculation we perform at Greentherm as part of the design and specification of your heating system. We ensure that your system will give you enough hot water to comfortably meet your daily needs, while still providing heat to your home, without the high fuel bills.

Now that we know how much water we need to store, how much space do we need to set aside to store it? That will be the subject of our next post.

The first in an upcoming series of short articles discussing the basics of design for your heating system, a comparison between boilers and heat pumps. What can each heat-source actually achieve?

We’ve already discussed the technical and physical side of heat pumps before. In summary, the higher the output temperature required, the less efficient the Heat Pump becomes. The Coefficient of Performance is a measure of the Heat Pump’s efficiency, the higher the better. The Hitachi Yutaki series of Heat-Pumps offered by Greentherm offer an approximate Coefficient of Performance of between 2 and 4 under normal operating conditions.

For the purposes of this article, we shall consider a standard gas-fired condensing boiler with a good efficiency rating of 90%. This means that 90% of the energy in the burned fuel is delivered as useable heat, with the other 10% lost.  Other boilers are reasonably similar, though with different efficiencies. Solid Fuel Boilers have certain specialised requirements that are beyond the scope of this article for the time being.

In the table below, Flow temperature is the maximum output water temperature from the Heat Pump or Boiler. Return temperature is the temperature of water returning to the Heat Pump. The maximum storage temperature will be somewhere between these values – less a small amount for losses in the cylinder heat-exchanger.

To demonstrate the effect this on system performance we will assume that both Heat Pump and Boiler are each connected to a 300 Litre domestic hot water cylinder with an ideally sized coil. The water in the cylinder is starting at a cold temperature of 10°C and needs to be raised to 50°C.

The time taken to heat the cylinder to temperature can be estimated and the approximate cost to heat the cylinder is then calculated using data available on the SEAI website here:*

The higher output temperatures, and greater delivered energy from the boiler heat the water much faster. Therefore, hot water will be available sooner from a boiler system from cold. A Heat Pump will take longer to deliver the same amount of heat. However, the cost of that energy from the heat-pump is a good deal less.  If night-rate electricity are used, the Heat Pump costs are halved. There is, however, no night rate available for gas.

Because it operates at a lower flow temperature the Heat Pump requires a larger heat-exchanger area within the cylinder to give good performance. Because of its higher flow temperatures, a boiler requires less coil area to achieve the same level of performance. This smaller coil is less efficient at transferring heat, requiring a larger temperature difference to be effective, meaning more heat can be lost within the system on the return to the boiler.

It must be remembered also that the above Heat Pump is operating in its least-efficient regime. It’s being asked to operate at its maximum rated heat output, a point at which the effective coefficient of performance will be closer to the minimum. To get to temperatures beyond this, an electric immersion heater or alternative heat-source would be required.

In truth, how often is hot water required at 50°C? For most washing water will be used at more comfortable temperatures below 30°C, so this store of hot water will likely be blended down with some cold water to achieve a desired comfortable temperature. The Heat Pump will operate far more efficiently if we allow it to work at a cooler temperature – say, 35°C.

Is there a way to meet our hot water demands using cooler water? This leads nicely into what will be the next post in this series:

Water Storage Temperatures and Why.

*As of September 2014. Energy Prices may vary.

At Greentherm, we sell the Grundfos Amazon  range of shower pumps. These are high-quality, quiet running shower pumps that are built to last. We’re often asked by Customers why they should consider an Amazon pump, in comparison to cheaper pumps on the market that might do the same job?

The simple truth is, because you want a shower pump that will last.

Shower pumps supplied by Greentherm are manufactured from potable-water quality materials. Pump housings and impellers are made from brass- a material which has good corrosion resistance and inherent antimicrobial capabilities. Brass kills germs and mold.

Why would you want potable-quality water coming from a shower?

Ultimately, because most people don’t wear masks while showering – there’s always the chance of accidentally swallowing shower water, so it needs to be safe to drink.

Furthermore, a metal housing for the pump allows it to run with high-temperature water safely. Water can be supplied a hot enough temperature to prevent the growth of Legionella bacteria – responsible for Legionnaire’s disease, then blended down with cold water at the shower head to ensure a comfortable and safe showering temperature.

Another advantage of a brass-bodied pump is durability. Plastic-bodies pumps will wear out faster than a metal pump. Exposure to hot water temperatures and the effects of ageing can embrittle plastics, leading to cracking, and premature failure and requiring a replacement. Not to mention, leaking hot water into your hot-press or utility room, then the cost of buying a new pump and the disruption required to install it.

A Grundfos Amazon shower pump will last for the life of your hot water system.

So what’s it like to live with?

Grundfos Amazon pumps are one of the quietest shower pumps available on the market today. Rubber mounting feet and flexible hose couplings minimise the transmission of noise through the building structure and through your plumbing.

Grundfos pumps are rated at 70dB, measured from a metre away from pump. Sound intensity decreases with the square of distance – meaning that every doubling of the distance between the observer and the pump, reduces the intensity of the sound by a factor of four. In the graph below, a drop of ten decibels represents a reduction in sound intensity by a factor of ten.

It’s clear then, that, when isolated from solid methods of transmission the noise from your high output shower pump will drop off rapidly.

The Thing to Remember.

Your home heating or hot-water system isn’t an iPhone. It’s not something that can be thrown away or replaced year-in, year-out for the latest model. It’s something that you want to have work, year-in, year-out, without ever giving you trouble.

A relatively small investment today – when compared to the cost of the entire system being replaced – will earn you years of peace-of-mind. This is something that will be part of your home for a long time to come. Peace of mind is priceless, after all.

Contact Us for more information on Shower Pumps.

 It’s a Tank, inside a Tank

With conventional buffer stores, domestic hot water is provided either through a plate heat exchanger, or a coil tapping within the buffer store. The limitations of this should be clear. The temperature of the domestic hot water is limited by the ability of the heat exchanger to transfer heat from from the buffer water, through the coil. With a high draw-off, cold water may flow faster than it can be heated, you may end up with lukewarm water at the taps. Or, you need higher cylinder temperatures, and correspondingly higher fuel use.

Greentherm Tank-in-Tank Cylinder Cutaway

A Greentherm Tank-in-Tank system saves you money.

Greentherm tank-in-tanks offer:

• Generic Pricing for Custom Cylinders.
  All Greentherm cylinders are custom made to your exact specifications. We deal directly with the manufacturer, cutting out the middlemen to ensure you get exactly what you need, at a price that suits your budget.

• 316L Stainless Steel Strength
  Domestic Hot Water tank manufactured from 316L Stainless Steel, for maximum resilience and corrosion resistance.

• Rapid recovery of domestic hot water with reduced cylinder temperatures.
  Domestic Hot Water tank is surrounded by heating system water, ensuring a rapid recovery of domestic hot water temperatures.

• Get the best out of your heating systems
  Allows multiple sources of heat to be combined into one store, capable of supplying both your central heating and domestic hot water ensuring no kilowatt-hour goes to waste. Operates at lower temperatures, for maximum efficiency.

• Flexible installation
  All Greentherm tank-in-tanks feature six configurable tappings in 1″ BSP, along with a single dedicated solar coil, allowing you to use any combination of heat sources in the one installation. Compatible with heat pumps, solid fuel boilers, solar panels and conventional boilers.

Introductory Offer:

Call us now to avail of special introductory pricing for the month of June.

Solar, Simplified with the Viridian Pod:

One of the costliest and most time-consuming jobs in any solar thermal retrofit, is fitting a new solar cylinder. The old cylinder must first be removed and disposed of, with central heating and hot-water systems being disconnected, before a new cylinder is fitted, then plumbed into place. Not to mention the lost space in the Hot Press which is consumed by a large hot water tank.

The Viridian Pod is a game-changing new approach that simplifies installation work, saving you time and effort. And saving the Hot Press.

Why Pod?

The Pod acts as a preheating buffer tank, supplying the existing domestic hot water cylinder in the home. Therefore:

• Plug and Play Technology
  Compatible with both Drainback and Pressurised Solar Panels. Pump station and controller integrated into one package. No unnecessary wiring. No time consuming plumbing work. It just Works.
• Discrete space saving design
  Horizontal design. Can be fitted into any attic or crawlspace. Can be located directly beneath the panels for maximum installation convenience.

• Fewer connections required. Robustness built in.
  No need to disassemble and rebuild the existing plumbing system to fit a new solar cylinder. Reduced potential for leaks requiring repairs and costly call backs, saving time.

• Compatible with any heating system.
  Preheated water can be supplied either to an existing domestic hot water cylinder or to a combi-boiler, simplifying system design. Custom designed systems are not required.
• Greentherm Recommends Viridian Clearline Solar Panels.
  Greentherm recommends matching Viridian Clearline Solar Panels with your Pod, for maximum compatibility and ease of installation.

• Special Introductory offer.
  Call now, at 01 5314781 to avail of introductory pricing on full system kits, and individual Pod systems.

Existing Cylinder

Combi-Boiler

The Viridian Pod saves you Time.

• Time designing.
• Time installing.
• Time commissioning.
• Time on maintenance and repair.

Contact us now for sales and technical inquiries.